1. Field of the Invention
The present invention relates to a process for forming a nonwoven sheet of composite aramid fibers, and aramid fibrid, using a foam furnish. More specifically, the present invention relates to an efficient foam process for making a uniform sheet of aramid fibers, also containing aramid fibrid.
2. Description of the Related Art
The use of foam in a furnish for preparing wet-laid, non-woven fibrous webs is known. See, for example, U.S. Pat. No. 4,443,297, which discloses an apparatus and method for the manufacture of a non-woven fibrous web using foam. The method involves preparing a foam furnish with 55-75% volume air, recirculating a surfactant-water solution through a forming wire followed by foam storage in a silo to eliminate excess air, and then recycling foam from the bottom of the silo. See also, U.S. Pat. Nos. 4,349,414; 4,443,299; 4,498,956; and 4,543,156.
U.S. Pat. No. 4,488,932 relates to a method of manufacturing fibrous webs of enhanced bulk. The method involves hammermilling dry hydrophilic fibers to generate crimp, and then foam forming these fibers in 0.5 to 5 minutes to retain as much crimp as possible.
U.S. Pat. No. 4,686,006 relates to an apparatus and method for laying down a fibrous web from a foam-fiber furnish. A headbox is used which includes walls defining an elongate channel extending transversely of the direction of movement of the forming wire. Foam forming nozzles are positioned to introduce foam-fiber furnish into the channel for turbulence, inducing impact on an oppositely disposed wall defining the channel. The turbulently flowing foam-fiber furnish is then introduced to the headbox slice for discharge onto the forming wire with minimized orientation of the fibers.
Other patents which relate to the use of foam in making non-woven fibrous webs include U.S. Pat. Nos. 3,716,449; 3,938,782; 3,871,952; 3,837,999; 3,876,498; 3,846,232; 4,062,721; 3,746,613, 4,056,456; 5,720,851; 5,904,809; 6,238,518 and 6,258,203.
Sheets of aramid fibers have been made. However, the formed sheets lack uniformly and the processes are inefficient. Moreover, the use of longer aramid fibers, e.g., longer than 0.25 inch, is desirable. Improved uniformity of dispersion and distribution of the aramid fibers in the web would be a great step forward in the art, as would increased ease and efficiency in forming the web, particularly when employing longer aramid fibers. Such sheets also containing aramid fibrid would be of great value. Techniques useful in the formation of more uniform non-woven webs made of longer aramid fibers would be of great benefit to the industry as such aramid fiber sheets have many potential uses, particularly when the sheet further contains aramid fibrid.
Accordingly, it is an object of the present invention to provide a novel process for forming a non-woven fibrous web of aramid fibers and aramid fibrid using foam, which process provides a web in which the fibers are uniformly and evenly distributed, and the web/sheet displays great integrity.
This and other objects and features of the invention will become apparent to one skilled in the art upon a review of the following description, the figures of the drawing, and the claims.